1. Field
The present disclosure relates to an electrophotographic photoreceptor used in the fields of copy machines, printers, or facsimile machines, etc, and an electrophotographic image forming apparatus and an electrophotographic cartridge using the electrophotographic photoreceptor.
2. Description of the Related Art
Electrophotographic devices such as facsimile machines, laser printers, copying machines, cathode ray tube (CRT) printers, liquid crystal printers, light-emitting diode (LED) printers, large plotters and laser electrophotographs and the like include an electrophotographic photoreceptor comprising a photosensitive layer formed on an electrically conductive substrate. The electrophotographic photoreceptor can be in the form of a plate, a disk, a sheet, a belt, a drum, or the like and forms an image as follows. First, a surface of the photosensitive layer is uniformly and electrostatically charged, and then the charged surface is exposed to a pattern of light, thus forming an image. The light exposure selectively dissipates the charge in the exposed regions where the light strikes the surface, thereby forming a pattern of charged and uncharged regions, which is referred to as a latent image. Then, a wet or dry toner is provided in the vicinity of the latent image, and toner droplets or particles collect in either the charged or uncharged regions to form a toner image on the surface of the photosensitive layer. The resulting toner image may be transferred to a suitable final or intermediate receiving surface, such as paper, or the photosensitive layer may function as the final receptor for receiving the image. Lastly, a residual electrostatic image on the surface of the photosensitive layer is removed by radiating light, emitted from an eraser lamp, on the surface of the photosensitive layer uniformly. Then, a small amount of residual toner left on the surface of the photosensitive layer is removed by using mechanical means such as a brush or blade.
A contact charging method is used as a charging method of an electrophotographic photoreceptor, instead of using a corona charging method. The contact charging method charges a surface of an electrophotographic photoreceptor to a predetermined electric potential by contacting the surface of the electrophotographic photoreceptor with a charging member such as an electrically conductive elastic roller in which direct voltages of about 1 KV to about 2 KV are applied from the outside.
The contact charging method may be classified into a direct current (DC) contact charging method, in which only a direct voltage is applied, and an alternating current (AC)/direct current (DC) contact charging method in which an alternating voltage is applied in superposition of a direct voltage. The DC contact charging method is advantageous in terms of increasing the lifetime of a developer, but is disadvantageous in that charge stains caused by non-uniform charging and discharge dielectric breakdown of an electrophotographic photoreceptor caused by direct application of a voltage may easily occur. Therefore, the AC/DC contact charging method is used mostly. However, a contact charging method, either a DC contact charging method or an AC/DC contact charging method, has limitations in that durability of a photoreceptor may decrease, for instance, a wear amount of a photoreceptor surface layer may increase. Therefore, with respect to a laminate type organic electrophotographic photoreceptor having a double-layer structured photosensitive layer including a charge generation layer (CGL) and a charge transport layer (CTL), the lifetime thereof is secured by using a method of increasing a thickness of the CTL. However, when the thickness of the CTL is increased, charge non-uniformity may be facilitated because charge capacity decreases and residual electric potential increases. When the charge non-uniformity occurs, reproducibility of an electrostatic latent image decreases and charge stains increase, and thus, high image quality and long lifetime may be hard to be compatible.
Therefore, in order to avoid charge stains in a laminate type electrophotographic photoreceptor, a method of removing charge stains is mainly selected, in which an electrostatic capacity is maximized by minimizing the thickness of a CTL in a range of about 9 μm to about 18 μm. For example, Japanese Patent Application Laid-Open Publication No. 2001-312082 aimed to obtain both high image quality and long lifetime by choosing a method of having a CTL thickness of about 9 μm to about 18 μm and also increasing an electrostatic capacity C for 1 cm2 of an electrophotographic photoreceptor to about 130 pF or more. However, when the thickness of the CTL is formed to be about 18 μm or less, the lifetime of the electrophotographic photoreceptor may be shortened.